Frequency, distribution and clinical management of incidental findings and extramedullary plasmacytomas in whole body diffusion weighted magnetic resonance imaging in patients with multiple myeloma

Quantitative assessment of bone marrow infiltration and characterization of tumor burden using dual-layer spectral CT in patients with multiple myeloma

BACKGROUND

The aim of the study was to evaluate whether virtual calcium subtraction (VNCa) image extracted from dual-layer spectral CT could estimate bone marrow (BM) infiltration with MRI as the reference standard and characterize tumor burden in patients with multiple myeloma (MM).

PATIENTS AND METHODS

Forty-seven patients with newly diagnosed MM were retrospectively enrolled. They had undergone whole-body low-dose dual-layer spectral CT (DLCT) and whole-body MRI within one week. VNCa images with calcium-suppressed (CaSupp) indices ranging from 25 to 95 at an interval of 10 and apparent diffusion coefficient (ADC) maps were quantitatively analyzed on vertebral bodies L1-L5 at the central slice of images. The optimal combination was selected by correlation analysis between CT numbers and ADC values. Then, it was used to characterize tumor burden by correlation analysis and receiver operating characteristic (ROC) curves analysis, including plasma cell infiltration rate (PCIR), high serum-free light chains (SFLC) ratio and the high-risk cytogenetic (HRC) status.

RESULTS

The most significant quantitative correlation between CT numbers of VNCa images and ADC values could be found at CaSupp index 85 for averaged L1-L5 (r = 0.612, p < 0.001). It allowed quantitative evaluation of PCIR (r = 0.835, p < 0.001). It could also anticipate high SFLC ratio and the HRC status with area under the curve (AUC) of 0.876 and 0.760, respectively.

CONCLUSIONS

The VNCa measurements of averaged L1-L5 showed the highest correlation with ADC at CaSupp index 85. It could therefore be used as additional imaging biomarker for non-invasive assessment of tumor burden if ADC is not feasible.

Renal Riddles Unveiled: Decoding Homogeneous Kidney Enlargement in Multiple Myeloma

Renal plasmacytoma is a rare extramedullary manifestation of plasma cell neoplasms (PCN). We present the case of a 62-year-old male with a history of relapsed refractory multiple myeloma (MM) who developed secondary renal plasmacytoma after an eight-year remission period. Radiological findings on plain CT raised concern for the most common renal malignancy, i.e. renal cell carcinoma (RCC), while further imagining evaluation with MRI suggested renal lymphoma, highlighting the diagnostic challenge of renal plasmacytoma on imagining. A renal mass biopsy confirmed a kappa-restricted plasma cell tumor, emphasizing the need for accurate differentiation between renal plasmacytoma and other renal malignancies to guide appropriate treatment strategies. Increased awareness of such cases can lead to timely recognition and tailored management for this rare entity.

Whole-body magnetic resonance imaging (WB-MRI) with diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) in prostate cancer: Prevalence and clinical significance of incidental findings

OBJECTIVE

Diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) is now recommended as a first-line staging modality in prostate cancer patients, and the widespread use of DWIBS may lead to an increased frequency of incidental findings. The aim of this study was to evaluate the prevalence and clinical significance of incidental findings on whole-body magnetic resonance imaging (WB-MRI) with DWIBS.

METHODS

Data from 124 patients with prostate cancer (age, 76.5 ± 5.6 years), who underwent 1.5 T WB-MRI with STIR, TSE-T2, TSE-T1, In/Out GRE, and DWIBS sequences, were retrospectively analyzed. Findings unrelated to prostate cancer were considered as incidental findings and categorized into two groups based on their clinical implications as follows: imaging follow-up or additional examinations was required (significant incidental findings) and no need to additional work-up (non-significant incidental findings). A chi-square test was performed to compare the differences in the prevalence of significant incidental findings based on age (≤75 and>75 years old).

RESULTS

A total of 334 incidental findings were found with 8.1% (n = 27) as significant incidental findings. Significant incidental findings were more frequent in patients over 75 years old than those of 75 years old or younger (28.6% vs  11.1%, p = 0.018).

CONCLUSION

Clinically significant incidental findings, which required imaging follow-up or additional examinations, were commonly observed in prostate cancer patients on WB-MRI/DWIBS.

ADVANCES IN KNOWLEDGE

Some incidental findings were clinically significant that may lead to changes in treatment strategy. Checking the entire organ carefully for abnormalities and reporting any incidental findings detected are important.

Review of diffusion-weighted imaging and dynamic contrast-enhanced MRI for multiple myeloma and its precursors (monoclonal gammopathy of undetermined significance and smouldering myeloma)

The last decades, increasing research has been conducted on dynamic contrast-enhanced and diffusion-weighted MRI techniques in multiple myeloma and its precursors. Apart from anatomical sequences which are prone to interpretation errors due to anatomical variants, other pathologies and subjective evaluation of signal intensities, dynamic contrast-enhanced and diffusion-weighted MRI provide additional information on microenvironmental changes in bone marrow and are helpful in the diagnosis, staging and follow-up of plasma cell dyscrasias. Diffusion-weighted imaging provides information on diffusion (restriction) of water molecules in bone marrow and in malignant infiltration. Qualitative evaluation by visually assessing images with different diffusion sensitising gradients and quantitative evaluation of the apparent diffusion coefficient are studied extensively. Dynamic contrast-enhanced imaging provides information on bone marrow vascularisation, perfusion, capillary resistance, vascular permeability and interstitial space, which are systematically altered in different disease stages and can be evaluated in a qualitative and a (semi-)quantitative manner. Both diffusion restriction and abnormal dynamic contrast-enhanced MRI parameters are early biomarkers of malignancy or disease progression in focal lesions or in regions with diffuse abnormal signal intensities. The added value for both techniques lies in better detection and/or characterisation of abnormal bone marrow otherwise missed or misdiagnosed on anatomical MRI sequences. Increased detection rates of focal lesions or diffuse bone marrow infiltration upstage patients to higher disease stages, provide earlier access to therapy and slower disease progression and allow closer monitoring of high-risk patients. Despite promising results, variations in imaging protocols, scanner types and post-processing methods are large, thus hampering universal applicability and reproducibility of quantitative imaging parameters. The myeloma response assessment and diagnosis system and the international myeloma working group provide a systematic multicentre approach on imaging and propose which parameters to use in multiple myeloma and its precursors in an attempt to overcome the pitfalls of dynamic contrast-enhanced and diffusion-weighted imaging.Single sentence summary statementDiffusion-weighted imaging and dynamic contrast-enhanced MRI provide important additional information to standard anatomical MRI techniques for diagnosis, staging and follow-up of patients with plasma cell dyscrasias, although some precautions should be taken on standardisation of imaging protocols to improve reproducibility and application in multiple centres.

Prospective Evaluation of Whole-Body MRI versus FDG PET/CT for Lesion Detection in Participants with Myeloma

Purpose To compare disease detection of myeloma using contemporary whole-body (WB) MRI and fluorine 18 (18F) fluorodeoxyglucose (FDG) PET/CT protocols and to correlate imaging with laboratory estimates of disease burden, including molecular characteristics. Materials and Methods In this observational, prospective study, participants were recruited from November 2015 to March 2018 who had a diagnosis of myeloma, who were planned to undergo chemotherapy and autologous stem cell transplantation, and who underwent baseline WB-MRI and FDG PET/CT (ClinicalTrials.gov identifier NCT02403102). Baseline clinical data, including genetics, were collected. Paired methods were used to compare burden and patterns of disease. Results Sixty participants (mean age, 60 years ± 9 [standard deviation]; 35 men) underwent baseline WB-MRI and FDG PET/CT. WB-MRI showed significantly higher detection for focal lesions at all anatomic sites (except ribs, scapulae, and clavicles) and for diffuse disease at all sites. Two participants presented with two or more focal lesions smaller than 5 mm only at WB-MRI but not FDG PET/CT. Participants with diffuse disease at MRI had higher plasma cell infiltration (percentage of nucleated cells: median, 60% [interquartile range {IQR}, 50%-61%] vs 15% [IQR, 4%-50%]; P = .03) and paraprotein levels (median, 32.0 g/L [IQR, 24.0-48.0 g/L] vs 20.0 g/L [IQR, 12.0-22.6 g/L]; P = .02) compared with those without diffuse disease. All genetically high-risk tumors showed diffuse infiltration at WB-MRI. Conclusion WB-MRI helped detect a higher number of myeloma lesions than FDG PET/CT, and diffuse disease detected at WB-MRI correlated with laboratory measures of disease burden and molecular markers of risk. Keywords: MR-Imaging, Skeletal-Appendicular, Skeletal-Axial, Bone Marrow, Hematologic Diseases, Oncology Clinical trial registration no. NCT02403102. Supplemental material is available for this article. © RSNA, 2021.

Extramedullary Plasmacytoma Causing Myelopathy Resulting in Gait Imbalance

Plasmacytomas are neoplasms of plasma cells that can involve the bone marrow, the bone itself, or soft tissue without bone marrow involvement. Extramedullary plasmacytomas are most commonly found in the upper respiratory tract in a total of 80% of all cases. Extramedullary plasmacytomas have also been documented in locations such as the central nervous system. This form of plasmacytoma may be seen as a solitary entity or in patients with multiple myeloma. We present a case of a 66-year-old female with a history of multiple myeloma on maintenance therapy with lenalidomide who has been experiencing gait imbalance for the past two months. The patient had a thoracic MRI done that revealed a mass at T7-8 with associated cord compression. She was taken for surgical intervention by neurosurgery. Pathology revealed trabecular bone and cartilage infiltrated by sheets of plasma cells highlighted by immunostaining CD138, monoclonal lambda light chains, consistent with a plasma cell neoplasm (plasmacytoma). The patient’s hospital course was complicated by hypotension resulting in transient ischemic myelopathy that was addressed in the neuro-intensive care unit. The patient was then discharged to an inpatient rehabilitation center. She would follow up with her primary oncologist for localized radiation therapy.

Whole-body MRI: a practical guide for imaging patients with malignant bone disease

Whole-body magnetic resonance imaging (MRI) is now a crucial tool for the assessment of the extent of systemic malignant bone disease and response to treatment, and forms part of national and international recommendations for imaging patients with myeloma or metastatic prostate cancer. Recent developments in scanners have enabled acquisition of good-quality whole-body MRI data within 45 minutes on modern MRI systems from all main manufacturers. This provides complimentary morphological and functional whole-body imaging; however, lack of prior experience and acquisition times required can act as a barrier to adoption in busy radiology departments. This article aims to tackle the former by reviewing the indications and providing guidance for technical delivery and clinical interpretation of whole-body MRI for patients with malignant bone disease.

MUKnine OPTIMUM protocol: a screening study to identify high-risk patients with multiple myeloma suitable for novel treatment approaches combined with a phase II study evaluating optimised combination of biological therapy in newly diagnosed high-risk multiple myeloma and plasma cell leukaemia

INTRODUCTION

Multiple myeloma (MM) is a plasma cell tumour with over 5800 new cases each year in the UK. The introduction of biological therapies has improved outcomes for the majority of patients with MM, but in approximately 20% of patients the tumour is characterised by genetic changes which confer a significantly poorer prognosis, generally termed high-risk (HR) MM. It is important to diagnose these genetic changes early and identify more effective first-line treatment options for these patients.

METHODS AND ANALYSIS

The Myeloma UK nine OPTIMUM trial (MUKnine) evaluates novel treatment strategies for patients with HRMM. Patients with suspected or newly diagnosed MM, fit for intensive therapy, are offered participation in a tumour genetic screening protocol (MUKnine a), with primary endpoint proportion of patients with molecular screening performed within 8 weeks. Patients identified as molecularly HR are invited into the phase II, single-arm, multicentre trial (MUKnine b) investigating an intensive treatment schedule comprising bortezomib, lenalidomide, daratumumab, low-dose cyclophosphamide and dexamethasone, with single high-dose melphalan and autologous stem cell transplantation (ASCT) followed by combination consolidation and maintenance therapy. MUKnine b primary endpoints are minimal residual disease (MRD) at day 100 post-ASCT and progression-free survival. Secondary endpoints include response, safety and quality of life. The trial uses a Bayesian decision rule to determine if this treatment strategy is sufficiently active for further study. Patients identified as not having HR disease receive standard treatment and are followed up in a cohort study. Exploratory studies include longitudinal whole-body diffusion-weighted MRI for imaging MRD testing.

ETHICS AND DISSEMINATION

Ethics approval London South East Research Ethics Committee (Ref: 17/LO/0022, 17/LO/0023). Results of studies will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ISRCTN16847817, May 2017; Pre-results.

Pictorial review of whole body MRI in myeloma: emphasis on diffusion-weighted imaging

There have been major advances in myeloma imaging over the past few years with focal lesions on imaging now forming part of the disease defining criteria. Whole body diffusion-weighted MRI (WB-MRI) is considered the most sensitive technique for the detection of focal active lesions. This pictorial review will focus on imaging the spectrum of myelomatous disorders on WB-MRI including diffusion and Dixon sequences. The typical imaging patterns of disease are demonstrated including in the contexts of staging, presumed solitary plasmacytoma, smouldering myeloma and examples of paramedullary and extramedullary disease. The utility of diffusion-weighted imaging in response assessment is a major advantage and this will be exemplified here.

Role of computed tomography texture analysis using dual-energy-based bone marrow imaging for multiple myeloma characterization: comparison with histology and established serologic parameters

Objective

To identify textural features on dual-energy CT (DECT)–based bone marrow images in myeloma which correlate with serum markers of myeloma activity and the degree of medullary involvement.

Methods

A total of 110 patients (63.0 ± 11.0 years, 51 female) who underwent unenhanced whole-body DECT between September 2015 and February 2019 were retrospectively included, which was approved by our institutional ethics committee with a waiver of the informed consent requirement. All patients had current hematologic laboratory tests. Using DECT post-processing, non-calcium bone marrow images were reconstructed. The vertebral bodies T10–L5 were segmented for quantification of textural features, which were compared with serologic parameters and myeloma stages by the Mann-Whitney U test. In a subgroup of 56/110 patients with current bone marrow biopsies, textural features were correlated with the degree of bone marrow infiltration.

Results

First-order features were higher in patients with advanced stage of myeloma (p < .02), whereas the 2nd-order “gray-level co-occurrence matrix (GLCM) cluster prominence” was lower (p < .04). In patients with elevated serum-free light chains (SFLC) or kappa/lambda SFLC ratio above 1.56, the “entropy” and 2nd-order GLCM features were lower (p < .03). The degree of bone marrow infiltration correlated with 1st-order features (e.g., “uniformity”; r_P = 0.49; p < .0001), whereas “entropy” and 2nd-order GLCM features were negatively correlated (e.g., “difference entropy”; r_P = − 0.54; p < .0001).

Conclusions

CT textural features applied on non-calcium bone marrow images correlate well with myeloma-related serologic parameters and histology showing a more uniform tissue structure and higher attenuation with increasing medullary infiltration and could therefore be used as additional imaging biomarkers for non-invasive assessment of medullary involvement.

Key Points

• Texture analysis applied on dual-energy reconstructed non-calcium bone marrow images provides information about marrow structure and attenuation.

• Myeloma-related serologic parameters and the degree of myeloma cell infiltration correlate with 1st- and 2nd-order features which could be useful as additional imaging biomarkers for non-invasive assessment of medullary involvement.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-07320-8) contains supplementary material, which is available to authorized users.

Extended Texture Analysis of Non-Enhanced Whole-Body MRI Image Data for Response Assessment in Multiple Myeloma Patients Undergoing Systemic Therapy

Identifying MRI-based radiomics features capable to assess response to systemic treatment in multiple myeloma (MM) patients. Retrospective analysis of whole-body MR-image data in 67 consecutive stage III MM patients (40 men; mean age, 60.4 years). Bone marrow involvement was evaluated using a standardized MR-imaging protocol consisting of T1w-, short-tau inversion recovery- (STIR-) and diffusion-weighted-imaging (DWI) sequences. Ninety-two radiomics features were evaluated, both in focally and diffusely involved bone marrow. Volumes of interest (VOI) were used. Response to treatment was classified according to International Myeloma Working Group (IMWG) criteria in complete response (CR), very-good and/or partial response (VGPR + PR), and non-response (stable disease (SD) and progressive disease (PD)). According to the IMWG-criteria, response categories were CR (n = 35), VGPR + PR (n = 19), and non-responders (n = 13). On apparent diffusion coefficient (ADC)-maps, gray-level small size matrix small area emphasis (Gray Level Size Zone (GLSZM) small area emphasis (SAE)) significantly correlated with CR (p < 0.001), whereas GLSZM non-uniformity normalized (NUN) significantly (p < 0.008) with VGPR/PR in focal medullary lesions (FL), whereas in diffuse involvement, 1st order root mean squared significantly (p < 0.001) correlated with CR, whereas for VGPR/PR Log (gray-level run-length matrix (GLRLM) Short Run High Gray Level Emphasis) proved significant (p < 0.003). On T1w, GLRLM NUN significantly (p < 0.002) correlated with CR in FL, whereas gray-level co-occurrence matric (GLCM) informational measure of correlation (Imc1) significantly (p < 0.04) correlated with VGPR/PR. For diffuse myeloma involvement, neighboring gray-tone difference matrix (NGTDM) contrast and 1st order skewness were significantly associated with CR and VGPR/PR (p < 0.001 for both). On STIR-images, CR correlated with gray-level co-occurrence matrix (GLCM) Informational Measure of Correlation (IMC) 1 (p < 0.001) in FL and 1st order mean absolute deviation in diffusely involved bone marrow (p < 0.001). VGPR/PR correlated at best in FL with GSZLM size zone NUN (p < 0.019) and in all other involved medullary areas with GLSZM large area low gray level emphasis (p < 0.001). GLSZM large area low gray level emphasis also significantly correlated with the degree of bone marrow infiltration assessed histologically (p = 0.006). GLCM IMC 1 proved significant throughout T1w/STIR sequences, whereas GLSZM NUN in STIR and ADC. MRI-based texture features proved significant to assess clinical and hematological response (CR, VPGR, and PR) in multiple myeloma patients undergoing systemic treatment.

Comparison of Whole-Body DWI and 18F-FDG PET/CT for Detecting Intramedullary and Extramedullary Lesions in Multiple Myeloma

OBJECTIVE. The purpose of this study was to compare the ability of whole-body (WB) DWI and ¹⁸F-FDG PET/CT in detecting intramedullary and extramedullary lesions in multiple myeloma. MATERIALS AND METHODS. The study included 49 patients with multiple myeloma who had undergone WB DWI and PET/CT. Intramedullary lesions for each region were scored by a scoring system using WB DWI and PET/CT separately. Extramedullary lesions seen separately on WB DWI and PET/CT per patient were recorded. Patients with diffuse lesions of the whole spine seen using both modalities were defined as group A, and those with such lesions seen on WB DWI only were defined as group B. The mean scores assigned to intramedullary lesions using the two modalities, the numbers of extramedullary lesions detected by WB DWI and PET/CT, and the mean percentages of plasma cells in the two patient groups were compared. RESULTS. Scores were higher for WB DWI than for PET/CT in all regions of the body (p < 0.05) except the skull, both in patients with a new diagnosis of multiple myeloma and in previously treated patients. Mean (± SD) percentages of plasma cells were significantly higher in group A than group B (50.458% ± 16.036% vs 18.682% ± 15.524%; p = 0.00). The mean number of extramedullary lesions detected by WB DWI was slightly higher than the mean number detected by PET/CT, although there was no statistical difference (4.48 ± 6.70 vs 4.39 ± 6.46 lesions; p = 0.86). CONCLUSION. For detecting intramedullary lesions, WB DWI is more sensitive than PET/CT in all regions except the skull, both in patients with a new diagnosis and previously treated patients and especially in patients with a low percentage of plasma cells. For detecting extramedullary lesions, WB DWI has sensitivity equivalent to that of PET/CT. The use of both modalities may offer complementary information.

Detection of avascular necrosis on routine diffusion-weighted whole body MRI in patients with multiple myeloma

OBJECTIVE

Current therapies for multiple myeloma, which include corticosteroids, increase risk of avascular necrosis. The aim of this study was to assess incidental detection of femoral head avascular necrosis on routine whole body MRI including diffusion weighted MRI.

METHODS

All whole body MRI studies, performed on patients with known multiple myeloma between 1 January 2010 to 1 May 2017 were assessed for features of avascular necrosis.

RESULTS

650 whole body MR scans were analysed. 15 patients (6.6%) had typical MR features of avascular necrosis: 2/15 (13.3%) had femoral head collapse, 4/15 (26.7%) had bilateral avascular necrosis and 9/15 (60%) were asymptomatic.

CONCLUSION

This is the first report of avascular necrosis detected on routine whole body MRI in patients with multiple myeloma. Targeted review of femoral heads in multiple myeloma patients undergoing whole body MR is recommended, including in patients without symptoms.

ADVANCES IN KNOWLEDGE

Whole body MR which includes diffusion-weighted MRI is extremely sensitive for evaluation of bone marrow. Although whole body MRI is primarily used for evaluation of multiple myeloma disease burden, it also presents an unique opportunity to evaluate the femoral heads for signs of avascular necrosis which can predate symptoms.

Imaging in multiple myeloma: How? When?

Bone disease is the most frequent feature of multiple myeloma (MM) and represents a marker of end-organ damage; it is used to establish the diagnosis and to dictate the immediate need for therapy. For this reason, imaging plays a significant role in the management of MM patients. Although conventional radiography has traditionally been the standard imaging modality, its low sensitivity in detecting osteolytic lesions and inability to evaluate response to therapy has called for the use of more sophisticated techniques, such as whole-body low-dose computed tomography (WBLDCT), whole-body magnetic resonance imaging, and ¹⁸F-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT). In this review, the advantages, indications of use, and applications of the 3 techniques in the management of patients with MM in different settings will be discussed. The European Myeloma Network and the European Society for Medical Oncology guidelines have recommended WBLDCT as the imaging modality of choice for the initial assessment of MM-related lytic bone lesions. Magnetic resonance imaging is the gold-standard imaging modality for detection of bone marrow involvement, whereas PET/CT provides valuable prognostic data and is the preferred technique for assessment of response to therapy. Standardization of most of the techniques is ongoing.

Implementing diffusion-weighted MRI for body imaging in prospective multicentre trials: current considerations and future perspectives

For body imaging, diffusion-weighted MRI may be used for tumour detection, staging, prognostic information, assessing response and follow-up. Disease detection and staging involve qualitative, subjective assessment of images, whereas for prognosis, progression or response, quantitative evaluation of the apparent diffusion coefficient (ADC) is required. Validation and qualification of ADC in multicentre trials involves examination of i) technical performance to determine biomarker bias and reproducibility and ii) biological performance to interrogate a specific aspect of biology or to forecast outcome. Unfortunately, the variety of acquisition and analysis methodologies employed at different centres make ADC values non-comparable between them. This invalidates implementation in multicentre trials and limits utility of ADC as a biomarker. This article reviews the factors contributing to ADC variability in terms of data acquisition and analysis. Hardware and software considerations are discussed when implementing standardised protocols across multi-vendor platforms together with methods for quality assurance and quality control. Processes of data collection, archiving, curation, analysis, central reading and handling incidental findings are considered in the conduct of multicentre trials. Data protection and good clinical practice are essential prerequisites. Developing international consensus of procedures is critical to successful validation if ADC is to become a useful biomarker in oncology.

KEY POINTS

• Standardised acquisition/analysis allows quantification of imaging biomarkers in multicentre trials. • Establishing "precision" of the measurement in the multicentre context is essential. • A repository with traceable data of known provenance promotes further research.

Whole-Body MRI: Current Applications in Oncology

OBJECTIVE

The purpose of this article is to review current image acquisition and interpretation for whole-body MRI, clinical applications, and the emerging roles in oncologic imaging, especially in the assessment of bone marrow diseases.

CONCLUSION

Whole-body MRI is an emerging technique used for early diagnosis, staging, and assessment of therapeutic response in oncology. The improved accessibility and advances in technology, including widely available sequences (Dixon and DWI), have accelerated its deployment and acceptance in clinical practice.

The Role of Minimal Residual Disease Testing in Myeloma Treatment Selection and Drug Development: Current Value and Future Applications

Treatment of myeloma has benefited from the introduction of more effective and better tolerated agents, improvements in supportive care, better understanding of disease biology, revision of diagnostic criteria, and new sensitive and specific tools for disease prognostication and management. Assessment of minimal residual disease (MRD) in response to therapy is one of these tools, as longer progression-free survival (PFS) is seen consistently among patients who have achieved MRD negativity. Current therapies lead to unprecedented frequency and depth of response, and next-generation flow and sequencing methods to measure MRD in bone marrow are in use and being developed with sensitivities in the range of 10^-5 to 10^-6 cells. These technologies may be combined with functional imaging to detect MRD outside of bone marrow. Moreover, immune profiling methods are being developed to better understand the immune environment in myeloma and response to immunomodulatory agents while methods for molecular profiling of myeloma cells and circulating DNA in blood are also emerging. With the continued development and standardization of these methodologies, MRD has high potential for use in gaining new drug approvals in myeloma. The FDA has outlined two pathways by which MRD could be qualified as a surrogate endpoint for clinical studies directed at obtaining accelerated approval for new myeloma drugs. Most importantly, better understanding of MRD should also contribute to better treatment monitoring. Potentially, MRD status could be used as a prognostic factor for making treatment decisions and for informing timing of therapeutic interventions. Clin Cancer Res; 23(15); 3980-93. ©2017 AACR.